In storage-area-network (SAN) environments, applications running on host systems (e.g., computers such as open system and/or mainframe servers) may be configured to access data in one or more volumes. These volumes may reside on storage devices, such as disk drives, tape drives, or the like. The applications may access data on (i.e., read or write to) the storage devices using a standard such as SCSI.
Because several applications running either on the same or different host systems may access data on the same volumes, data coherency can become an important issue. That is, in certain cases, an application needs to be able to determine whether other applications have modified or altered the data on the volume since the application last accessed the data on the volume. This can be particularly important with volumes stored on tape drives or other sequential-access storage media devices.
If an application can quickly establish coherency (i.e., determine that the data was not modified since it was last accessed by the application), the application can trust the integrity of the data and perform operations on the data accordingly. On the other hand, if the application cannot establish coherency, the application may not be able to trust the integrity of the data. In such cases, the application may need to read all or a substantial part of the data on the volume to verify the integrity of the data and/or learn what is actually stored on the volume. This can be a very time-consuming and inefficient process.
In view of the foregoing, what is needed is a system and method for quickly determining the coherency of a volume. Such a determination ideally could be made with little or no inspection of data on the volume. Further needed are systems and methods to make sequential-access storage media, such as magnetic tape, more self-describing.